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 A small clinical trial of a late-liver-stage attenuated malaria parasite vaccine has shown to be safe and effective against the disease spread by mosquitoes and claims 608,000 lives globally. 

The trial, led by researchers at Leiden University Medical Center and Radboud University Medical Center in Netherlands, found that immunisation with a genetically modified Plasmodium falciparum parasite, known as GA2, induced a favorable immune response, while also protecting against infection.

For the trial, the team randomly assigned 25 healthy adult volunteers with no prior malaria exposure to receive immunisation with a genetically modified P. falciparum parasite (GA2) -- designed to continue developing longer in the liver. 

While 10 participants were assigned to the GA2 group, another 10 were added to the GA1 group, and five to the placebo group. Each group consisted of both male and female volunteers.

Three immunisation sessions at 28-day intervals involved exposure to 50 mosquitoes infected with the respective parasites or uninfected in the case of the placebo group. 

Three weeks after the final immunisation, all participants were exposed to controlled human malaria infection to evaluate protective efficacy.

The results published in the New England Journal of Medicine, showed that protective efficacy was observed in 89 per cent people in the GA2 group. Only 13 per cent in the GA1 group had the prtoective effect whuile those administered the placebo group had none. 

Further, the team also found no breakthrough infections occurred after exposure to GA2, indicating a strong safety profile.  

The GA2 participants also exhibited a strong proinflammatory response. Both GA2 and GA1 also induced similar antibody titers against the P. falciparum circumsporozoite protein. 

This suggests that the enhanced protection with GA2 is associated with cellular immune responses rather than antibody levels alone, the researchers said.